A passage structure for PEM fuel cells is configured locally differently in order to adapt the flow of gas on the membrane electrode assembly (MEA). Starting from the cathode entry port, the active gas volumetric flow per unit area on the MEA is locally varied by changing the number and/or cross section of the gas-carrying passages, so that the flow decreases toward the cathode exit port. Suitable configuration of the passage structure according to the invention allows the steam partial pressure to be optimally matched to the local conditions. The mass conversion is improved in these regions as a result without the electrolyte's drying out. At locations in the flowfield with a low gas humidity, the measures according to the invention (increased number of passages or passage width) significantly reduce the flow velocity. As a result, the transfer of water from the MEA to the gas flow is reduced and drying of the MEA is diminished.